There are few descriptions of movement disorders as an initial presentation of acquired immunodeficiency syndrome (AIDS). The authors report the case of a 54-year-old man who presented with hemiballismus of gradual onset. The computed axial tomographic scan showed a deep seated enhancing lesion with mass effect. Investigation revealed AIDS and a probable toxoplasmosis. It is concluded that AIDS must be considered in the aetiological diagnosis of patients with movement disorders.